version 1.17, 2002/08/22 20:07:33
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version 1.33, 2008/10/08 20:54:09
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Line 10 This manual is for Vmgen
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Line 10 This manual is for Vmgen
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(version @value{VERSION}, @value{UPDATED}), |
(version @value{VERSION}, @value{UPDATED}), |
the virtual machine interpreter generator |
the virtual machine interpreter generator |
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Copyright @copyright{} 2002 Free Software Foundation, Inc. |
Copyright @copyright{} 2002,2003,2005,2007 Free Software Foundation, Inc. |
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@quotation |
@quotation |
Permission is granted to copy, distribute and/or modify this document |
Permission is granted to copy, distribute and/or modify this document |
under the terms of the GNU Free Documentation License, Version 1.1 or |
under the terms of the GNU Free Documentation License, Version 1.2 or |
any later version published by the Free Software Foundation; with no |
any later version published by the Free Software Foundation; with no |
Invariant Sections, with the Front-Cover texts being ``A GNU Manual,'' |
Invariant Sections, with the Front-Cover texts being ``A GNU Manual,'' |
and with the Back-Cover Texts as in (a) below. A copy of the |
and with the Back-Cover Texts as in (a) below. A copy of the |
Line 27 Software Foundation raise funds for GNU
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Line 27 Software Foundation raise funds for GNU
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@end quotation |
@end quotation |
@end copying |
@end copying |
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@dircategory GNU programming tools |
@dircategory Software development |
@direntry |
@direntry |
* Vmgen: (vmgen). Interpreter generator |
* Vmgen: (vmgen). Virtual machine interpreter generator |
@end direntry |
@end direntry |
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@titlepage |
@titlepage |
Line 85 Input File Format
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Line 85 Input File Format
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* Input File Grammar:: |
* Input File Grammar:: |
* Simple instructions:: |
* Simple instructions:: |
* Superinstructions:: |
* Superinstructions:: |
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* Store Optimization:: |
* Register Machines:: How to define register VM instructions |
* Register Machines:: How to define register VM instructions |
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Input File Grammar |
Input File Grammar |
Line 93 Input File Grammar
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Line 94 Input File Grammar
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Simple instructions |
Simple instructions |
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* Explicit stack access:: If the C code accesses a stack pointer |
* C Code Macros:: Macros recognized by Vmgen |
* C Code Macros:: Macros recognized by Vmgen |
* C Code restrictions:: Vmgen makes assumptions about C code |
* C Code restrictions:: Vmgen makes assumptions about C code |
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* Stack growth direction:: is configurable per stack |
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Using the generated code |
Using the generated code |
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Line 328 instructions. Another option is to use
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Line 331 instructions. Another option is to use
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for the virtual machine; we believe that using a stack architecture is |
for the virtual machine; we believe that using a stack architecture is |
usually both simpler and faster. |
usually both simpler and faster. |
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however, this option is slower or |
However, this option is slower or |
significantly more complex to implement than a stack machine architecture. |
significantly more complex to implement than a stack machine architecture. |
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Vmgen has special support and optimizations for stack VMs, making their |
Vmgen has special support and optimizations for stack VMs, making their |
Line 605 Most examples are taken from the example
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Line 608 Most examples are taken from the example
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* Input File Grammar:: |
* Input File Grammar:: |
* Simple instructions:: |
* Simple instructions:: |
* Superinstructions:: |
* Superinstructions:: |
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* Store Optimization:: |
* Register Machines:: How to define register VM instructions |
* Register Machines:: How to define register VM instructions |
@end menu |
@end menu |
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Line 707 text according to the following grammar;
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Line 711 text according to the following grammar;
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Forth you need for using Vmgen: |
Forth you need for using Vmgen: |
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@example |
@example |
text: stack-decl|type-prefix-decl|stack-prefix-decl |
text: stack-decl|type-prefix-decl|stack-prefix-decl|set-flag |
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stack-decl: 'stack ' ident ident ident |
stack-decl: 'stack ' ident ident ident |
type-prefix-decl: |
type-prefix-decl: |
's" ' string '" ' ('single'|'double') ident 'type-prefix' ident |
's" ' string '" ' ('single'|'double') ident 'type-prefix' ident |
stack-prefix-decl: ident 'stack-prefix' string |
stack-prefix-decl: ident 'stack-prefix' string |
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set-flag: ('store-optimization'|'include-skipped-insts') ('on'|'off') |
@end example |
@end example |
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Note that the syntax of this code is not checked thoroughly (there are |
Note that the syntax of this code is not checked thoroughly (there are |
Line 732 are:
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Line 737 are:
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@findex single |
@findex single |
@findex double |
@findex double |
@findex stack-prefix |
@findex stack-prefix |
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@findex store-optimization |
@example |
@example |
stack ( "name" "pointer" "type" -- ) |
stack ( "name" "pointer" "type" -- ) |
( name execution: -- stack ) |
( name execution: -- stack ) |
type-prefix ( addr u item-size stack "prefix" -- ) |
type-prefix ( addr u item-size stack "prefix" -- ) |
single ( -- item-size ) |
single ( -- item-size ) |
double ( -- item-size ) |
double ( -- item-size ) |
stack-prefix ( stack "prefix" -- ) |
stack-prefix ( stack "prefix" -- ) |
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store-optimization ( -- addr ) |
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include-skipped-insts ( -- addr ) |
@end example |
@end example |
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An @var{item-size} takes three cells on the stack. |
An @var{item-size} takes three cells on the stack. |
Line 798 Before we can use @code{data-stack} in t
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Line 806 Before we can use @code{data-stack} in t
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@cindex stack basic type |
@cindex stack basic type |
@cindex basic type of a stack |
@cindex basic type of a stack |
@cindex type of a stack, basic |
@cindex type of a stack, basic |
@cindex stack growth direction |
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This line defines the stack @code{data-stack}, which uses the stack |
This line defines the stack @code{data-stack}, which uses the stack |
pointer @code{sp}, and each item has the basic type @code{Cell}; other |
pointer @code{sp}, and each item has the basic type @code{Cell}; other |
types have to fit into one or two @code{Cell}s (depending on whether the |
types have to fit into one or two @code{Cell}s (depending on whether the |
type is @code{single} or @code{double} wide), and are cast from and to |
type is @code{single} or @code{double} wide), and are cast from and to |
Cells on accessing the @code{data-stack} with type cast macros |
Cells on accessing the @code{data-stack} with type cast macros |
(@pxref{VM engine}). Stacks grow towards lower addresses in |
(@pxref{VM engine}). By default, stacks grow towards lower addresses in |
Vmgen-erated interpreters. |
Vmgen-erated interpreters (@pxref{Stack growth direction}). |
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@cindex stack prefix |
@cindex stack prefix |
@cindex prefix, stack |
@cindex prefix, stack |
Line 823 name. Stack prefixes are defined like t
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Line 830 name. Stack prefixes are defined like t
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@example |
@example |
\E inst-stream stack-prefix # |
\E inst-stream stack-prefix # |
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\E data-stack stack-prefix S: |
@end example |
@end example |
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This definition defines that the stack prefix @code{#} specifies the |
This definition defines that the stack prefix @code{#} specifies the |
Line 839 If there are multiple instruction stream
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Line 847 If there are multiple instruction stream
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first one (just as the intuition suggests). |
first one (just as the intuition suggests). |
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@menu |
@menu |
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* Explicit stack access:: If the C code accesses a stack pointer |
* C Code Macros:: Macros recognized by Vmgen |
* C Code Macros:: Macros recognized by Vmgen |
* C Code restrictions:: Vmgen makes assumptions about C code |
* C Code restrictions:: Vmgen makes assumptions about C code |
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* Stack growth direction:: is configurable per stack |
@end menu |
@end menu |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node C Code Macros, C Code restrictions, Simple instructions, Simple instructions |
@node Explicit stack access, C Code Macros, Simple instructions, Simple instructions |
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@subsection Explicit stack access |
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@cindex stack access, explicit |
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@cindex Stack pointer access |
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@cindex explicit stack access |
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This feature is not needed and not supported in the 0.6.2 version of |
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vmgen that is documented here (and that is invoked by default). |
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Not all stack effects can be specified using the stack effect |
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specifications above. For VM instructions that have other stack |
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effects, you can specify them explicitly by accessing the stack |
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pointer in the C code; however, you have to notify Vmgen of such |
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explicit stack accesses, otherwise Vmgens optimizations could conflict |
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with your explicit stack accesses. |
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You notify Vmgen by putting @code{...} with the appropriate stack |
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prefix into the stack comment. Then the VM instruction will first |
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take the other stack items specified in the stack effect into C |
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variables, then make sure that all other stack items for that stack |
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are in memory, and that the stack pointer for the stack points to the |
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top-of-stack (by default, unless you change the stack access |
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transformation: @pxref{Stack growth direction}). |
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The general rule is: If you mention a stack pointer in the C code of a |
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VM instruction, you should put a @code{...} for that stack in the stack |
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effect. |
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Consider this example: |
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@example |
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return ( #iadjust S:... target afp i1 -- i2 ) |
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SET_IP(target); |
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sp = (Cell *)(((char *)sp)+iadjust); |
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fp = afp; |
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i2=i1; |
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@end example |
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First the variables @code{target afp i1} are popped off the stack, |
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then the stack pointer @code{sp} is set correctly for the new stack |
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depth, then the C code changes the stack depth and does other things, |
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and finally @code{i2} is pushed on the stack with the new depth. |
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The position of the @code{...} within the stack effect does not |
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matter. You can use several @code{...}s, for different stacks, and |
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also several for the same stack (that has no additional effect). If |
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you use @code{...} without a stack prefix, this specifies all the |
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stacks except the instruction stream. |
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You cannot use @code{...} for the instruction stream, but that is not |
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necessary: At the start of the C code, @code{IP} points to the start |
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of the next VM instruction (i.e., right beyond the end of the current |
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VM instruction), and you can change the instruction pointer with |
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@code{SET_IP} (@pxref{VM engine}). |
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@c -------------------------------------------------------------------- |
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@node C Code Macros, C Code restrictions, Explicit stack access, Simple instructions |
@subsection C Code Macros |
@subsection C Code Macros |
@cindex macros recognized by Vmgen |
@cindex macros recognized by Vmgen |
@cindex basic block, VM level |
@cindex basic block, VM level |
Line 899 if (branch_condition) @{
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Line 966 if (branch_condition) @{
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SUPER_CONTINUE; |
SUPER_CONTINUE; |
@end example |
@end example |
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@c !! uncomment for post-0.6.2 docs |
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@c @item VM_JUMP |
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@c @findex VM_JUMP |
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@c @code{VM_JUMP(target)} is equivalent to @code{goto *(target)}, but |
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@c allows Vmgen to do dynamic superinstructions and replication. You |
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@c still need to say @code{SUPER_END}. Also, the goto only happens at |
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@c the end (wherever the VM_JUMP is). Essentially, this just suppresses |
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@c much of the ordinary dispatch mechanism. |
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@end table |
@end table |
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Note that Vmgen is not smart about C-level tokenization, comments, |
Note that Vmgen is not smart about C-level tokenization, comments, |
Line 910 a C preprocessor macro.
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Line 986 a C preprocessor macro.
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node C Code restrictions, , C Code Macros, Simple instructions |
@node C Code restrictions, Stack growth direction, C Code Macros, Simple instructions |
@subsection C Code restrictions |
@subsection C Code restrictions |
@cindex C code restrictions |
@cindex C code restrictions |
@cindex restrictions on C code |
@cindex restrictions on C code |
Line 970 macros can be implemented in several way
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Line 1046 macros can be implemented in several way
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@samp{IP} points to the next instruction, and @samp{IPTOS} is its |
@samp{IP} points to the next instruction, and @samp{IPTOS} is its |
contents. |
contents. |
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@c -------------------------------------------------------------------- |
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@node Stack growth direction, , C Code restrictions, Simple instructions |
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@subsection Stack growth direction |
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@cindex stack growth direction |
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@cindex @code{stack-access-transform} |
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By default, the stacks grow towards lower addresses. You can change |
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this for a stack by setting the @code{stack-access-transform} field of |
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the stack to an xt @code{( itemnum -- index )} that performs the |
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appropriate index transformation. |
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E.g., if you want to let @code{data-stack} grow towards higher |
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addresses, with the stack pointer always pointing just beyond the |
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top-of-stack, use this right after defining @code{data-stack}: |
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@example |
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\E : sp-access-transform ( itemnum -- index ) negate 1- ; |
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\E ' sp-access-transform ' data-stack >body stack-access-transform ! |
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@end example |
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This means that @code{sp-access-transform} will be used to generate |
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indexes for accessing @code{data-stack}. The definition of |
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@code{sp-access-transform} above transforms n into -n-1, e.g, 1 into -2. |
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This will access the 0th data-stack element (top-of-stack) at sp[-1], |
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the 1st at sp[-2], etc., which is the typical way upward-growing |
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stacks are used. If you need a different transform and do not know |
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enough Forth to program it, let me know. |
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@c -------------------------------------------------------------------- |
@c -------------------------------------------------------------------- |
@node Superinstructions, Register Machines, Simple instructions, Input File Format |
@node Superinstructions, Store Optimization, Simple instructions, Input File Format |
@section Superinstructions |
@section Superinstructions |
@cindex superinstructions, defining |
@cindex superinstructions, defining |
@cindex defining superinstructions |
@cindex defining superinstructions |
Line 1029 accesses a stack pointer should not be u
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Line 1132 accesses a stack pointer should not be u
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does not check these restrictions, they just result in bugs in your |
does not check these restrictions, they just result in bugs in your |
interpreter. |
interpreter. |
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@cindex include-skipped-insts |
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The Vmgen flag @code{include-skipped-insts} influences superinstruction |
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code generation. Currently there is no support in the peephole |
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optimizer for both variations, so leave this flag alone for now. |
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@c ------------------------------------------------------------------- |
@c ------------------------------------------------------------------- |
@node Register Machines, , Superinstructions, Input File Format |
@node Store Optimization, Register Machines, Superinstructions, Input File Format |
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@section Store Optimization |
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@cindex store optimization |
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@cindex optimization, stack stores |
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@cindex stack stores, optimization |
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@cindex eliminating stack stores |
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This minor optimization (0.6%--0.8% reduction in executed instructions |
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for Gforth) puts additional requirements on the instruction descriptions |
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and is therefore disabled by default. |
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What does it do? Consider an instruction like |
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@example |
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dup ( n -- n n ) |
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@end example |
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For simplicity, also assume that we are not caching the top-of-stack in |
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a register. Now, the C code for dup first loads @code{n} from the |
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stack, and then stores it twice to the stack, one time to the address |
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where it came from; that time is unnecessary, but gcc does not optimize |
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it away, so vmgen can do it instead (if you turn on the store |
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optimization). |
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Vmgen uses the stack item's name to determine if the stack item contains |
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the same value as it did at the start. Therefore, if you use the store |
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optimization, you have to ensure that stack items that have the same |
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name on input and output also have the same value, and are not changed |
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in the C code you supply. I.e., the following code could fail if you |
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turn on the store optimization: |
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@example |
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add1 ( n -- n ) |
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n++; |
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@end example |
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Instead, you have to use different names, i.e.: |
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@example |
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add1 ( n1 -- n2 ) |
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n2=n1+1; |
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@end example |
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Similarly, the store optimization assumes that the stack pointer is only |
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changed by Vmgen-erated code. If your C code changes the stack pointer, |
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use different names in input and output stack items to avoid a (probably |
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wrong) store optimization, or turn the store optimization off for this |
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VM instruction. |
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To turn on the store optimization, write |
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@example |
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\E store-optimization on |
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@end example |
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at the start of the file. You can turn this optimization on or off |
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between any two VM instruction descriptions. For turning it off again, |
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you can use |
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@example |
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\E store-optimization off |
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@end example |
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@c ------------------------------------------------------------------- |
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@node Register Machines, , Store Optimization, Input File Format |
@section Register Machines |
@section Register Machines |
@cindex Register VM |
@cindex Register VM |
@cindex Superinstructions for register VMs |
@cindex Superinstructions for register VMs |
Line 1100 You have used an instruction-stream pref
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Line 1272 You have used an instruction-stream pref
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side). |
side). |
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@cindex @code{prefix for this combination must be defined earlier} error |
@cindex @code{prefix for this combination must be defined earlier} error |
@item the prefix for this combination must be defined earlier |
@item the prefix for this superinstruction must be defined earlier |
You have defined a superinstruction (e.g. @code{abc = a b c}) without |
You have defined a superinstruction (e.g. @code{abc = a b c}) without |
defining its direct prefix (e.g., @code{ab = a b}), |
defining its direct prefix (e.g., @code{ab = a b}), |
@xref{Superinstructions}. |
@xref{Superinstructions}. |
Line 1114 expected by Vmgen (this should not happe
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Line 1286 expected by Vmgen (this should not happe
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line in a bug report). |
line in a bug report). |
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@cindex @code{syntax error, wrong char} error |
@cindex @code{syntax error, wrong char} error |
@cindex syntax error, wrong char |
@item syntax error, wrong char |
A syntax error. If you do not see right away where the error is, it may |
A syntax error. If you do not see right away where the error is, it may |
be helpful to check the following: Did you put an empty line in a VM |
be helpful to check the following: Did you put an empty line in a VM |
instruction where the C code is not delimited by braces (then the empty |
instruction where the C code is not delimited by braces (then the empty |
Line 1133 The stack item does not match any define
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Line 1305 The stack item does not match any define
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away any stack prefix). You should either declare the type prefix you |
away any stack prefix). You should either declare the type prefix you |
want for that stack item, or use a different type prefix |
want for that stack item, or use a different type prefix |
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@item @code{unknown primitive} error |
@cindex @code{unknown primitive} error |
@item unknown primitive |
@item unknown primitive |
You have used the name of a simple VM instruction in a superinstruction |
You have used the name of a simple VM instruction in a superinstruction |
definition without defining the simple VM instruction first. |
definition without defining the simple VM instruction first. |
Line 1323 type. For @samp{inst-stream}, the name
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Line 1495 type. For @samp{inst-stream}, the name
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plain r-value; typically it is a macro that abstracts away the |
plain r-value; typically it is a macro that abstracts away the |
differences between the various implementations of @code{NEXT_P*}. |
differences between the various implementations of @code{NEXT_P*}. |
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@cindex IMM_ARG |
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@findex IMM_ARG |
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@item IMM_ARG(access,value) |
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Define this to expland to ``(access)''. This is just a placeholder for |
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future extensions. |
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@cindex top of stack caching |
@cindex top of stack caching |
@cindex stack caching |
@cindex stack caching |
@cindex TOS |
@cindex TOS |
Line 1352 profiling.
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Line 1530 profiling.
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@item SUPER_CONTINUE |
@item SUPER_CONTINUE |
This is just a hint to Vmgen and does nothing at the C level. |
This is just a hint to Vmgen and does nothing at the C level. |
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@findex MAYBE_UNUSED |
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@item MAYBE_UNUSED |
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This should be defined as @code{__attribute__((unused))} for gcc-2.7 and |
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higher. It suppresses the warnings about unused variables in the code |
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for superinstructions. You need to define this only if you are using |
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superinstructions. |
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@findex VM_DEBUG |
@findex VM_DEBUG |
@item VM_DEBUG |
@item VM_DEBUG |
If this is defined, the tracing code will be compiled in (slower |
If this is defined, the tracing code will be compiled in (slower |
Line 1529 instruction instead of laying down @code
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Line 1714 instruction instead of laying down @code
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The code for peephole optimization is in @file{vmgen-ex/peephole.c}. |
The code for peephole optimization is in @file{vmgen-ex/peephole.c}. |
You can use this file almost verbatim. Vmgen generates |
You can use this file almost verbatim. Vmgen generates |
@file{@var{file}-peephole.i} which contains data for the peephoile |
@file{@var{file}-peephole.i} which contains data for the peephole |
optimizer. |
optimizer. |
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@findex init_peeptable |
@findex init_peeptable |
Line 1723 a major change, and it's ramifications a
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Line 1908 a major change, and it's ramifications a
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@chapter The future |
@chapter The future |
@cindex future ideas |
@cindex future ideas |
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We have a number of ideas for future versions of Gforth. However, there |
We have a number of ideas for future versions of Vmgen. However, there |
are so many possible things to do that we would like some feedback from |
are so many possible things to do that we would like some feedback from |
you. What are you doing with Vmgen, what features are you missing, and |
you. What are you doing with Vmgen, what features are you missing, and |
why? |
why? |
Line 1746 please let us know.
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Line 1931 please let us know.
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@chapter Changes |
@chapter Changes |
@cindex Changes from old versions |
@cindex Changes from old versions |
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Use-visible changes between 0.5.9-20010501 and 0.5.9-20020822: |
User-visible changes between 0.5.9-20020822 and 0.5.9-20020901: |
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The store optimization is now disabled by default, but can be enabled by |
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the user (@pxref{Store Optimization}). Documentation for this |
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optimization is also new. |
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User-visible changes between 0.5.9-20010501 and 0.5.9-20020822: |
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There is now a manual (in info, HTML, Postscript, or plain text format). |
There is now a manual (in info, HTML, Postscript, or plain text format). |
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Line 1809 You can find vmgen information at
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Line 2000 You can find vmgen information at
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* GNU Free Documentation License:: License for copying this manual. |
* GNU Free Documentation License:: License for copying this manual. |
@end menu |
@end menu |
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@node GNU Free Documentation License, , Copying This Manual, Copying This Manual |
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@appendixsec GNU Free Documentation License |
@include fdl.texi |
@include fdl.texi |
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